The androgen-dependent growth of human prostate cancer is well documented, as is the use of androgen ablation as a therapeutic maneuver. Dihydrotestosterone has a much higher affinity for the androgen receptor and is thus a more potent ligand. 5- - reductase catalyzes the conversion of testosterone and has 2 isoforms. The existing approved inhibitor of 5- -reductase, finasteride, inhibits primarily the Type II isoform, primarily located on fibromuscular stromal cells. Prostatic epithelial cells, which are the cell of origin of prostatic adenocarcinoma, primarily express Type I receptors, and would more likely be inhibited by a pure, or mixed type I inhibitor. LY300502 represents the first such compound, and will be tested as an oral, 3X daily dosing over a 12-week period to patients with prostate cancer as either first or second-line hormonal therapy. This phase I trial will involve 32 patients at 3 institutions (Indiana university, University of Colorado, and University of Pittsburgh) and will test 4 different dose levels of the drug with classic pharmacokinetic sampling. In addition, levels of testosterone and dihydrotestosterone will be measured to measure the level of inhibition of 5- -reductase, since maximal inhibition may take place at a dose level that does not produce side effects. This dose will then be taken into a subsequent phase II trial.